This application is based on application Nos. 10-281709 and 10-289140 filed in Japan, the contents of which are hereby incorporated by reference.
(1) Field of the Invention
The present invention relates to a data receiving device that receives serial data, a data transmitting apparatus that transmits the serial data, a method of transmitting the serial data, and an image forming apparatus that forms images using the transmitted data.
(2) Description of Related Art
Conventionally, a clock synchronization method has been used for data transmission in an image forming apparatus, for instance, when an image is read using an image reader and data of the image is transmitted from an image reading unit that creates the image data to an image forming unit. According to the clock synchronization method, two transmission paths, a data line and a clock line, are used, through which image data and clock signals are transmitted, respectively. Image data that has been transmitted through the data line is received using clock signals that have been transmitted through the clock line from the sending end.
According to the conventional clock synchronization method, however, the two transmission paths (including a transmission buffer, a wiring unit, and a reception buffer) from the data sending end to the data receiving end have a difference in amount of delay (referred to a xe2x80x9cskewxe2x80x9d in this specification). Under the circumstance, when the transmission rate is equal to or greater than several tens of megabits per second, the skew is too large to be neglected and data transmission is not assured.
On the other hand, high-speed and multifunctional copying machines have recently increased the amount of information to be transmitted. As a result, electromagnetic waves are radiated from a harness that transmits data at a high speed. In order to prevent the radiation of electromagnetic waves, expensive devices such as optical fibers may be used on the transmission path. In this case, it is desirable to use as small number of optical fibers as possible for a lower cost.
It is accordingly an object of the present invention to provide a data receiving device, a data transmitting apparatus, and a data transmitting method that realize a high-speed data transmission at a lower cost.
Another object of the present invention is to provide an image forming apparatus that forms images using image data that has been transmitted by and according to the data receiving device, the data transmitting apparatus, and the data transmitting method.
The above-mentioned first object may be achieved by a data receiving device that may include: a receiving unit for receiving image data and synchronous data that have been alternately transmitted from a sending end; a receiving clock generator for generating a receiving clock signal for latching data to be received; a PLL circuit for synchronizing phases of the generated receiving clock signal and the synchronous data; and a controller for stopping the PLL circuit synchronizing the phases while the receiving unit is receiving the image data.
In the data receiving device, phase synchronization of the receiving clock, which has been generated at the receiving end, is performed while the synchronous data is being received, and the image data can be received using the receiving clock. As a result, it is not necessary to provide different transmission paths for the synchronous data and the image data, so that a lower-cost, high-speed data transmission can be realized.
The first object may be also achieved by a data transmitting apparatus that may include: a data sending device that includes a sending unit for sending a plurality of frames of serial data which each include synchronous data and effective data; and a data receiving device that includes (1) a receiving unit for receiving the serial data, (2) a receiving clock generator for generating a receiving clock signal, (3) a frequency divider for dividing frequency of the receiving clock signal and generating a divided clock signal, (4) a PLL circuit for synchronizing phases of the generated divided clock signal and the received synchronous data, and (5) a controller for stopping the PLL circuit synchronizing the phases while the effective data is being received.
The first object may be also achieved by a data transmitting method in a data transmitting apparatus that includes a data sending device that sends a plurality of frames of serial data which each include synchronous data and effective data, and a data receiving device that receives the serial data, the data transmitting method may include: a phase synchronizing step for synchronizing phases of the synchronous data that has been received by the data receiving device and a receiving clock signal that has been generated in the data receiving device; and a phase synchronization stopping step for stopping the phase synchronization before reception of the effective data.
The above-mentioned second object may be achieved by an image forming apparatus that may include: a data receiving device that includes, a receiving unit for receiving image data and synchronous data that have been alternately transmitted from a sending end, a receiving clock generator for generating a receiving clock signal for latching data to be received, a PLL circuit for synchronizing phases of the generated receiving clock signal and the synchronous data, and a controller for stopping the PLL circuit synchronizing the phases while the receiving unit is receiving the image data; and an image forming unit for forming images according to the received image data.